1. Field of the Invention
This invention relates to emergency alarm systems, and more particularly to alarm systems having both audible and visual signal devices located remotely from a master control panel.
2. Description of the Related Art
It is generally recognized that conventional fire alarm control panels have now been developed to the point where they are considered to be highly reliable. In buildings protected by such panels, when an alarm is sounded the occupants readily acknowledge the existence of a potential danger and quickly vacate the premises. However, many such conventional alarm systems give no indication of the severity of the danger, nor where the danger point is, or what would be the best course of action to pursue, as well as whether or not the alarm might be false. A situation having variables such as these could result in either inaction, or improper action and unnecessary injury.
The above drawback has been recognized, and improvements have been made by replacing the electromechanical bells and horns with loud speakers, and by providing an electronically-generated alarm signal, such as a siren, with a capability for voice over ride whereby a qualified person can communicate important information to the building occupants in an emergency situation.
There exist several methods of upgrading an existing alarm system to one having both alarm signal and voice capabilities. One approach is to completely scrap the existing alarm panel and replace it with a modernized one having the desired voice amplification and speaker circuitry. However, this is usually very costly. An alternative is to add an adapter module which can provide the desired combined voice and signal capabilities while still retaining the advantages of alarm detection and circuitry supervision of the already existing alarm control panel.
The present invention relates to improvements in the alarm apparatus disclosed and claimed in my U.S. Pat. No. 4,703,312 dated Oct. 27, 1987.
This patented device was intended for use with two-wire systems having loud speakers connected at the desired points along the wires. A signal generator and amplifier were provided, for producing a "whoop" type sound, namely a swept 400-1400 Hz wave that had a pulse repetition rate of about one second.
In addition to this, a voice-override capability was built into the system, wherein operation of a microphone button silenced the signal generator if it was active, and enabled the transmission of verbal messages over the speakers. Transmission of verbal messages under non-alarm conditions was also featured.
In some installations it is desired to have both an audible warning system, and a visual warning system, the latter usually taking the form of a flashing light, which periodically produces high-intensity light pulses. This usually meant the use of a 4-wire system, two being for transmission of the audio, and the remaining two carrying d.c., for the flashing light. Such requirements presented only minor problems when the wiring was being installed at the time during which a building was under construction. However, for existing buildings and alarm installations having exclusively two-conductor lines, the addition of the flashing light meant re-wiring of the entire complex, which was both costly and time-consuming.
Examples of existing audio/visual alarms are shown in U.S. Pat. Nos. 4,274,084; 4,101,880; and 4,258,332.
In U.S. Pat. No. 4,274,084, there is disclosed a circuit for producing periodic flashes of light, generated by a neon-triggered flashtube, and in addition, synchronized bursts from a bell or chime. The circuit has no provision for disabling either mode of alarm while permitting the other to remain active. Nor is there any provision for transmission of voice messages.
U.S. Pat. No. 4,101,880 relates to an audio-visual alarm circuit which produces flashes every one-half second or so, and a continuous "horn" sound that fluctuates in amplitude, or "pulses" with each flash. No provision is made for disabling either mode of alarm. Also, transmission of voice messages is not possible with this system.
U.S. Pat. No. 4,258,332 involves an alarm system employing multiple remotely located combination amplifier/loud speaker units which are fed by means of a 2-wire line. Provision is made for transmitting both siren-type alarm signals and voice communication. The line is fed with d.c. of sufficient amplitude to provide supply power for each amplifier; in addition, under alarm conditions, a small a.c. component containing the audio that is to be transmitted is superimposed on, or employed to "modulate" the d.c. component. At each unit, the relatively small a.c. component is separated from the d.c. and amplified by the respective amplifier. Each amplifier drives a separate speaker. Separation is accomplished at the input of the unit, by means of a rectifier and choke which block the a.c. and pass only the d.c., and a blocking capacitor, which blocks the d.c. and passes only the a.c.
The primary disadvantage of this system is that where a relatively large number of remote amplifier/speaker units is employed, the power drain becomes excessive since each amplifier is drawing current at the same time. In the event that the system is to function during a failure of the 115 volt power mains (in which case battery back-up is employed), this power drain consideration becomes even more important. Also, the use of multiple amplifiers is deemed to be too costly, especially in view of the fact that in many current systems, there has been successfully employed only a single amplifier located at one location and having sufficient power to drive the desired number of remotely located speakers. Finally, it is believed that the reliability in such a multiple amplifier system is reduced, because the number of parts is greatly increased over that where a single amplifier is employed.
For the above reasons, it is believed that the patented device noted in the previous two paragraphs has not found wide acceptance in the industry.
Other systems are disclosed in the following patents: U.S. Pat. Nos. 3,309,685; 3,912,883; 3,611,362; 3,711,854; 3,936,821; 3,448,447; 3,569,964; and 3,618,081.
U.S. Pat. No. 3,309,685 discloses a supervised alarm circuit containing both visual and audible alarm components connected across a two-wire transmission line; no provision is made for selectively activating either visual or audible modes separately. U.S. Pat. No. 3,912,883 relates to a supervised alarm system having loud speakers connected across a two-wire line. U.S. Pat. Nos. 3,711,854, 3,448,447, 3,569,964, 3,618,081 and 3,611,362 all employ audible alarm devices, namely bells, whereas U.S. Pat. No. 3,936,821 discloses the use of either horns or bells.